An electromagnetic actuator that drives an intake valve and an exhaust valve of an internal combustion engine to open and close is disclosed in Japanese Patent Laid-Open Publication No. 2000-199411. For the internal combustion engine, it is demanded to reduce the time required for opening and closing the intake and exhaust valves during high-speed rotation and to increase the amount of valve lift.
In order to reduce the time for opening and closing the intake and exhaust valves, it is required to improve the speed of opening and closing the valves. The improvement of the speed requires an increase in force generated by the electromagnetic actuator, and therefore increasing the size of a magnet of a moving element of the actuator is one of resolutions to be considered.
However, increasing the size causes the weight of the moving element to be increased. Therefore, there occur problems such that it is difficult to obtain a desired speed of an opening-closing valve and to achieve a desired response of the opening-closing valve.
Moreover, in order to control high-speed response of the opening-closing valve, for example, electromagnetic energy has to be supplied to the electromagnetic actuator in a short period of 1 millisecond or 2 milliseconds. This requires a large amount of power. Therefore, this method has another problem in that an enormous amount of power is consumed.
The present invention has been achieved to solve the above-mentioned problems in the conventional technology. It is an object of this invention to provide an opening-closing valve driving apparatus having excellent responsivity, that is, to provide an opening-closing valve driving apparatus capable of ensuring a desired lift amount of the opening-closing valve and reducing power consumption of the electromagnetic actuator.